Railway signal control circuit



June 9, 1942. VH. G. BLossER RAILWAY SIGNAL CONTROL CIRCUIT Filed Dec.l0, 1940 4. IH I 19E.

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-H-efl illngl?! Maffei 150006Z@ y 1N i-:NToR Herma Zomer.

HIS ATTORNEY Time fzg. 2.

Patented June 9, 1.942

RAILWAY SIGNAL CONTROL CIRCUIT Herman G. Blosser, Pittsburgh, Pa.,assignox` to The Union Switch & Signal Company, Swissvale, Pa., acorporation of Pennsylvania Application December 10, 19,40, Serial No.369,439

11 Claims.

My invention relates to circuits for controlling railway signals and ithas special reference to the utilization by such circuits of the codedfeed back operating principle that first was disclosed by Frank H.Nicholson Patent No. 2,021,944 (issued November 26, 1935) and that alsois shown by numerous later patents and applications of common ownershipherewith.

Generally stated, the object of my invention is to increase the utilityand broaden the range of application of coded feed back control circuitsof both the track and the line type.

A more specific object is to prevent the off period energized detectorrelays of such circuits from being falsely picked up by storagepotential when the circuit conductors are by-passed and have only the onperiod pulses of master code energy impressed thereupon.

Another object is to provide improved means for prolonging each periodof detector relay pick-up for the full duration of the master code offperiod within which the pick-up occurs.

A further object is to improve the organization of the apparatus bywhich the master on period energy pulses and the feed back olfperiodenergy pulses are supplied to and received from the circuitconductors.

In practicing my invention, I attain the above and other objects andadvantages by: (1) supplementing the master coding device by a re- .l

peater relay which introduces a short delay between the end of eachmaster code on period and the subsequent off period connection of thefeed back energized detector relay with the circuit conductors; and (2)including a back contact of this repeater relay in the hold-upprolonging circuit for the detector relay.

I shall describe one form of coded feed back control circuit whichembodies my invention, and shall then point out the novel featuresthereof in claims. This illustrative embodiment is disclosed in theaccompanying drawing, in which:

Fig. l is a diagrammatic representation of a track type of controlcircuit that is equipped with the improved apparatus of my invention andthat is organized to form part of an automatic block signaling systemhaving coded feed back approach lighting control; and

Fig. 2 shows master and feed back codes for the circuit of Fig. l, andindicates the manner in which those codes are produced by joint relayoperation.

In the several views of the drawing, like reference characters designatecorresponding parts.

Referring rst to Fig. 1, the improved control circuit organization of myinvention is there disclosed in association with a coded track circuitsystem of automatic block signaling for a railway track I-2 over whichit Will be assumed that traiiic moves in the single direction indicatedby the arrow, or from left to right in the diagram. The protectedstretch of this track is divided into the customary successive sectionsby insulated rail joints 3 and the rails of each section form part of atrack type of control circuit which normally is capable of transmittingenergy between its two ends but which at times `is rendered incapable ofsuch transmission.

In this view of Fig. 1, reference characters D and E respectivelydesignate the entrance and the exit ends of one of these track sections(which illustratively is shown as being a full signal block in length);character TR designates a code following track relay which is installedat the entrance end of the section and operated by energy received fromthe rails thereof; charac- `ters BX-CX the terminals of an alternatingcurrent master energy source that is provided at the section exit forthe purpose of supplying these rails with the relay operating energyjust referred to; character CTM a coding device having a contact 5 whichcodes this energy by periodically interrupting the rail supply circuit;and character S the usual wayside signal which guards the entrance ofeach of the track blocks and which is controlled by the associated trackrelay TR through the medium of decoding apparatus H-J.

An automatic block signaling system of the referred to coded trackcircuit type operates without the aid of kline wires and in therepresentative form disclosed it includes all of the elements abovenamed. Such a system further comprises the customary facilities (notshown in Fig. 1) for continuously operating each of the exit end relaysCTM at one or another of the vusual plurality of distinctive vcoderates. Selection among these rates (which in a typical three-indicationsystem may consist of and 180 energy pulses per minute) is made inaccordance with advance trafc conditions by the decoding apparatus IPI-J`functioning in customary manner.

This decoding apparatus is controlled in the usual fashion by theassociated track relay TR and it performs the further function ofselectively setting up a lighting circuit for one or another of thesignal lamps (G, Y and R in the typical three-indication system abovereferred to) of the wayside signal S at the same location,

the rails of that rear section, the lamp lightingV circuits therefor arecarried over a back contact I2 of an approach relay AR that is installedat each of the signal locations D, E, etc. Each of these relays AR isslow releasing and as long as the winding thereof is recurrentlyenergized at code speed rate, contact I2 occupies the illustrated pickedup position wherein the signal circuits are disconnected from theirlighting supply source.

Controlling the energization of each of these approach relays AR is adetector relay KR installed at the section exit in the manner shown atlocation E and operating contacts I3-.I4 in the exciting and outputcircuits of a transformer 'AT through which pick-up current is at propertimes supplied to the approach relay. This arrangement of devicesKR-AT-AR embodies principles that are disclosed and claimed in acopending application Serial No. 210,744, filed May 28, 1938 by Frank H.Nicholson et al., now U. S. Patent 2,237,788, granted Apr. 8, 1941, andit results in relay AR holding contact I2 picked up as long as relay KRfollows code and in releasing contact I2 whenever relay KR ceases tofollow code.

The pick-up winding of the detector relay KR is connected with thesection rails duringI and only during the master code off periods. Thisconnection is established at the back points of contacts I6 and I'I of arelay CP which (as will be more completely described later) repeats theoperations of coding device CTM; it includes a full wave rectifier I8;and over it oiI period pulses of feed back energy are impressed upon thedetector relay as long as the section remains vacant. These pulsesrecurrently pick up contacts I3-I 4 and thereby cause the approach relayAR to keep signal Se deenergized.

These detector relay energizing pulses of feed back energy are suppliedto the section rails by apparatus that is installed at the entrancelocation D. This apparatus comprises: (1) a source of feed back energydesignated by the alternating current supply terminals BK-CK; (2) animpulse relay IR having contacts I9 and 20 for transferring theconnection of the section rails I-2 from the track relay TR to sourceBK-CK during each off period of the received master code; and (3) acircuit supplied from a winding 2I of the main decoding transformer DTover which a short pulse of pick-up current is impressed upon theimpulse relay IR at the beginning of each of the named off code periods.

The just named impulse relay IR may be of the same polarized type asthat shown and described by Patent No. 2,174,255 which issued to me onVSeptember 26, 1939, and which now is the subject of a reissueapplication Serial No. 3518,319, filed September 25, 1940, now U. S.Reissue Patent 21,783, granted April 29, 1941. As long as the -windingof this impulse relay remains deenergized or receives reverse polarityenergy, coning winding of track relay TR across the section rails by wayof a connection that includes a full wave rectifier 23 and a tracktransformer TD.

This connection is completed during each on period of the receivedmaster code. During each off period of the received master code,however, the decoding transformer winding 2| supplies the impulse relayIR with a short pulse of given polarity energy. Each of these pulsespicks up contacts I9-2 and by transferring the rail connection from therelay TR to the feed back source BK-CK causes energy from that sourcethen to be supplied to the section rails.

The coded feed back control circuit combination of Fig. 1 hasillustratively been shown as utilizing alternating current energy forthe operation thereof. As has now become apparent, this operating energyis supplied from the master and feed back sources BX-CX and BK-CK at thecircuit exit and entrance ends E and D.

Interposed between the master source and the section rails is a tracktransformer TE which during the on periods of the supplied master codefunctions as a step-down device, and which during the off code periodssteps up the potential of the received feed back energy to a valuesuitable for operating the detector relay KR. The earlier namedtransformer TD at the section entrance performs similar functions.During the off periods of the received master code it steps down thepotential of the rail supplied feed back energy from source BK--CK andduring the on periods of that code it steps up the received masterenergy to a potential suitable for operating the track relay TR.

The improvements of my invention reside in: (1) the interposition of therepeater relay CP between the master coding device CTM and therail-to-detector relay connection for the purpose of introducing a shortdelay between the end of each master on period and the subsequent offconnection of the detector relay with the section rails; and (2) aninclusion of a contact 25 of this repeater relay in the hold-upprolonging or stick circuit (later to be described) for the detectorrelay KR.

The improvements which the repeater relay CP effects will rst beconsidered. In the prior art organizations which the coded feed backcontrol circuits of my Patent 2,174,255 typify, the master codingcontact 5 is directly used to connect the feed back energized detectorrelay KR with the section rails I-2 during the master code off periods.With that arrangement, the detector relay connection is completed almostsimultaneously with the end of each master code on period.

In certain track circuit installations wherein that arrangement is used,difficulty has been experienced in keeping the detector relay KRcontinuously released during occupied section conditions. This dificultyhas its foundation in the accumulation between the section rails of astorage potential during each master code on period and the persistenceof this accumulated potential into the early portion of each succeedingoff code period.

When the detector relay KR was connected with the rails immediatelyafter the on period end, it received and in certain instances wasfalsely picked up by the remaining voltage of this storage energy. Evenwith a train in the track section, the detector relay KR was in thismanner continued in code following operation. In a system of the typeshown in Fig. 1, such a continuance is obviously objectionable in thatentry of a train into section D E, for example, is by it prevented fromreleasing approach relay AR and lighting signal Se in the intendedmanner.

To overcome this difculty, I have supplemented the conventional exit endorganization of track circuit apparatus by the repeater relay CP andhave arranged that this relay delay the connection of the detector relayKR until such a point in each master code off period as the trackstorage potential has died down to a value that is ineffective foroperating relay KR.

In the illustrative organization which Fig. l shows at location E, thisrepeater relay CP is energized from any suitable local source, such asis designated by the terminals plus and minus, over a pick-up circuitwhich includes a front contact 21 of the master coding device CTM. Thecontacts of relay CP thus repeat all pick-up and releasing operations ofcoding device 2l. That is, repeater contacts |6 l1 25 are picked up whencontacts 5 21 of device CTM are picked up and released when contacts 521 are released.

On each action, however, there is a delay on the part of the repeatingcontacts. Referring to Fig. 2, if the coding device contacts reach theirpicked up position at point a, then the repeater relay contacts willreach their picked up position at a slightly later point designated asb. Likewise, if the coding device contacts reach their released positionat point c, the repeater relay contacts will reach their releasedposition at the later point d.

Examining in greater detail the circuits of which contacts lG-ll ofrelay CP form a part, it will be seen that when these contacts arepicked up they complete the circuit over which master source BX-CXsupplies the section rails with -on period pulses of master code energy,and that During this delay, the storage potential present 3 in the trackrails at the end of the on code period has a chance to die down orentirely disappear and, in consequence, the detector relay KR cannotfalsely be picked up thereby.

The operation of my extended exit end facilities will have become moreor less apparent from the foregoing description of the structurecomprised thereby. Under both vacant and occupied conditions of tracksection D-E, the master coding relay CTM picks up and releases in theregularly recurring manner which the diagram of Fig. 2 represents, andthe repeater relay CP picks up and releases in delayed synchronism withthe master coding device, as points b and d of Fig. 2 show.

When the track section is vacant and devices CTM and CP are both pickedup, as shown at b e in Fig. 2, the exit end source ;BX CX energizes andpicks up the entrance end track relay TR over a circuit that includesfront contact 5 of device CTM, front contacts |6 |1 of device CP, thetrack transformer TE, the section rails 1 2, the track transformer TD,back contact I9 20 of device IR, rectifier 23 and the winding of relayTR. Upon, however, the release of either of the devices CTM or CP, asduring the time period e-f of Fig. 2, the master code supply circuit isinterrupted and at a later point, designated at g in Fig. 2 anddetermined by the relay charac- 75 teristics, the entrance end trackrelay TR releases.

Each such release causes decoding transformer DT to induce in winding 2|a pulse of energy which picks up the impulse relay IR at some point suchas shown at h in Fig. 2. Contacts [9 20 now transfer the rail connectionfrom relay TR to feed back source BK CK. While this connection iscompleted, or for time h m of Fig, 2, that entrance end source energizesand picks up the exit end detector relay KR over a circuit that includesfront contacts Ill-2D of device IR, transformer TD, the track rails 1 2,transformer TE, back contacts I6-I1 of relay CP, rectifier I8 and thewinding of relay KR.

The impulse relay IR is timed to release before the master coding deviceCTM picks up repeater relay CP to start, as at point f of Fig. 2,another master code on period. Because of this release timing, the pulseof feed back energy is terminated, as at point m of Fig. 2, and thetrack relay TR is reconnected with the section rails well in advance ofthat succeeding on period.

In the manner just explained the code producing movements of contact 5of master coding device CTM are reproduced by the entrance end relay TRand the off period pick-ups of the impulse relay IR are reproduced bythe exit end detector relay KR. These reproducing actions take place,quite obviously, only as long as the section D E remains vacant and therails 1 2 thereof are left free to transmit energy between the twocircuit ends.

Upon entry of a train into section D E, the resulting by-pass of rails I2 prevents master code energy from source BX-CX from reaching relay TRand also prevents feed back energy from source BK CK from reachingdetector relay KR. In consequence, both of these relays then are keptcontinuously released.

In the case of relay KR, this desired condition of continuous releasepersists even though the section rails I i. accumulate considerablestorage potential during each on period of the master code energy thatis supplied during occupied section conditions. The reason for thispersistence is the before described delay, designated at c d in Fig. 2,which the repeater relay CP introduces in each off period connection ofthe detector relay KR with the section rails.

The magnitude of this delay (c d of Fig. 2) will, ofcourse, vary withthe track circuit characteristics and may be adjusted by changing thedelay period of the repeater relay CP. For extreme cases of storageeffect, a comparatively long period may be required. For otherinstallations where the storage effect is less pronounced, a smallerdelay will be found adequate.

The expedients of my invention by which the hold-up time of the detectorrelay KR is prolonged will next be considered. As Fig. 2 shows, eachpulse of feed back energy which is supplied over the front points ofcontacts IS-ZS of the impulse relay IR has the comparatively shortlength that is designated by h m. Each of these feed back pulses picksup detector relay KR at a point therein such as is indicated at q inFig, 2. In the absence of hold-up prolonging means, the period of eachpick-up for the detector relay KR would obviously be exceedingly shortin comparison to the total length of the master code off period duringwhich that pick-up occurs.

Such extreme shortness of pick-up time is undesirable in that it means agreatly prolonged time of relay release. In the performance of controlfunctions such las involve the approach relay AR of Fig. 1, as close anapproximation as possible to equal pick-up and release times is much tobe desired.

To equalize the pick-up and release times of detector relay devices ofthe type which Fig. l shows at KR, it has been proposed to supplementthe relay pick-up circuit by a stick circuit which is completed from thetime of each pickup of the relay until the end of the on code periodduring which that pick-up occurs. One form which such a stick circuitmay take is` disclosed and claimed by Patent No. 2,172,893 which issuedto Edward U. Thomas on September 12, 1939.

As there shown, the detector relay stick circuit employs a front contactof the detector relay connected in series with a back contact of theassociated master coding device. In the improved arrangement of myinvention (see location E of Fig. 1) the corresponding stick circuitmakes use of a front contact 29 of the detector relay KR that isconnected in series with ,a back contact 25 of the repeater relay CP.

In this improved arrangement, cut-off of the stick circuit energizationis extended beyond the pick-up time t (Fig. 2) of the master codingdevice CTM and does not occur until the time n (Fig. 2) that therepeater relay CP picks up'. In consequence, the hold-up time of thedetector relay KR is prolonged to the order indicated at c in Fig. 2.

The matter in which my improved detector relay stick circuit operateswill now have become more or less apparent. During each master code oifperiod, contact 25 of relay CP is released and it sets the circuit up.Upon pick-up of contact 29 of relay KR the circuit is completed. Itextends from the positive terminal of a suitable supply source throughfront contact 29, conductor 30, back contact 25, conductor 3l and thewinding of relay KR back to the negative terminal of the supply source.

Once completed this stick circuit holds the detector relay continuouslypicked up until an interruption therein occurs. Such an interruption ismade at contact 25 upon pick-up of relay CP at the off period end. Thisallows relay KR to release at the later time 1J of Fig. 2.

Although the several improvements of my invention have been shown anddescribed as forming a part of a coded feed back control circuit of thetrack type, it will be obvious that these improvements are notrestricted thereto but that they also have utility when applied tocontrol circuit combinations of any other form wherein the conductorslose their normal energy transmitting capability under certainconditions only.

Thus, instead of being track rails as shown, the control circuitconductors l-2 may also Atake the form of line wires which connectmaster energy supply and feed back repeating equipment .(see devicesCTM-CP-KR at location E in Fig. 1) at one end of the circuit withAmaster energy receiving and feed back energy supply equipment (seedevices TR-IR-TD at location D in Fig. 1) at the other end of thecircuit.

When used with a control circuit of the line conductor type justdescribed, eachof the improvements herein disclosed will function inexactly the same manner as when used with the track type of controlcircuit that is herein illustrated. My invention is, therefore, one ofbroad utility and is not to be restricted to the specific form ofapplicationV that I have shown bywayof illustration. Y Y Y n Y From theforegoing description of Figs. 1 and 2, therefore, it will be seen thatI have made important contributions to control circuit com- Aloinationsvof the coded feed back class. In particular, I have increased theutility and broadened the range of application of such circuits; I haveprevented thefoif period energized detector relays frombeing falselypicked up by storage potential when the circuit conductors are by-passedand have only the on period pulses of master code energy impressedthereon; I have provided improved means for prolonging each period ofdetector relay pick-up for the full duration of the master code foifperiod within which the pick-up occurs; and I have improved theorganization of the apparatus by which the master code on period energypulses and the feed back off period energy pulses are supplied to andreceived from the circuit conductors.

Although I Vhave herein shown and described only one form of railwaytraiiic controlling apparatus embodying my invention, it is understoodthat various changes and modifications maybe made therein Within thescope of the appended claims without departing from the spirit and scopeof my invention.

Having thus described my invention, what I claim is: l

1. In combination, a control circuit comprising a pair of conductorswhich normally are capable of transmitting energy between given andopposite ends of said circuit but which at times are rendered incapableof such transmission, means including a coding device at the given endof said circuit for supplying said conductors with master code energy inthe form of recurring on period pulses that are separated by oi periodintervals, means governed by the said pulses of master energy that arereceived at the opposite end of said circuit for there further supplyingsaid conductors with feed back energy in the form of pulses that recurin step With said master code off periods, a detector relay at saidgiven circuit end for distinguishing between said normal or energytransmitting conditions of said circuit conductors and non-transmittingconditions thereof, and means controlled by said coding device for (1)connecting said detector relay with said conductors during each of saidmaster code off periods whereby under said energy transmittingconditions of those conductors the detector relay receives and respondsto the said pulses of feed back energy which the conductors thentransmit and (2) maintaining said detector relay disconnected from saidconductors during each of said master code on periods plus the earlyportion `of each following off period whereby at all times the detectorrelay is prevented from receiving either the master energy of said onperiod pulses or the master energy potential that under non-transmittingY as well as transmitting conditions of said circuit period intervals,means governed by the said pulses of master energy that are received atthe opposite end of said circuit for there further supplying saidconductors with feed back energy in the form of pulses that recur instep with said master code off periods, a detector relay at said givencircuit end for distinguishing between said normal or energytransmitting condition of said circuit conductors and. non-transmittingconditions thereof, a repeater relayv controlled by said coding deviceand occupying a rst position during each of said master code on periodsbut shifting after a short delay to a second position upon the occasionof eachof said master code off periods, and means including a contact ofsaid repeater relay that is closed in said second position and open insaid first position for connecting said detector relay with saidconductors during and only during the concluding portion of each of saidmaster code off periods whereby under said energy transmittingconditions of those conductors the detector relay receives and respondsto the said pulses of feed back energy which the conductors thentransmit and whereby at all times the detector relay is prevented fromreceiving master energy storage potential that under non-transmitting asWell as transmitting conditions of said circuit may be stored in saidconductors at the beginning of each of said off code periods.

3. In combination, a control circuit comprising alpair of conductorswhich normally are capable of transmitting energy but which at times arerendered incapable of such transmission, a coding device having contactswhich shift from a front to a back position and from said back to saidfront position repeatedly and in synchronous relation with respect toeach other, a repeater relay energized over one of said coding devicecontacts and being picked up when that contact is in its front positionbut releasing after a short delay upon each transfer of that contact toits back position, a source of master energy for said circuit, aconnection which is completed only when another of said coding devicecontacts is in its front position at a time when a contact of saidrepeater relay is picked up and over which said circuit conductors aresupplied with master code energy that is derived from said master sourceand that is in the form of recurring on period pulses that are separatedby off periodsintervals, means governed by said on period pulses ofmaster energy for further supplying said conductors with feed backenergy in the form of pulses that recur in step with said master codeoff periods, a detector relay for distinguishing between said energytransmitting and said non-transmitting conditions of said circuitconductors, and a connection of said detector relay with said conductorswhich includes a back contact of said repeater relay and which iscompleted duringand only during each of said master code off periods butnot until after the initial portion thereof whereby under said circuittransmitting conditions the detector relay receives and responds to thesaid pulses of feed back energy which the circuit conductors thentransmit and whereby at all times the detector relay is prevented fromreceiving master energy storage potential that under saidnon-transmitting as well as said transmitting conditions of said circuitmay be present between said conductors during the early portion of eachof said off code periods.

4. In combination, a section of railway track,

means including a coding device for supplying the rails of said-sectionwith master code energy in the form of recurring on period pulses thatare separated by off period intervals, means' effective under vacantconditions of said section and governed by said on period master energypulses for further supplying said rails with feed back energy in theform of pulses that recur in step with said master code off periods, adetector relay for distinguishing between vacant and occupied conditionsof said section, and means controlled by said coding device forconnecting said detector relay with said rails during and only duringthe concluding portion of each of said master code off periods wherebyunder said vacant section conditions the detector relay receives andresponds to the said pulses of feed back energy which those rails thentransmit and whereby at all times the detector relay is prevented fromreceiving master energy storage potential that under occupied as well asvacant conditions of said section may be present between said railsduring the early portion of each of said off code periods.

5. In combination, a section of railway track, means including a codingdevice for supplying the rails of said section with master code energyin the form of recurring on period pulses that are separated by offperiod intervals, means effective under vacant conditions of saidsection and governed by said on period master energy pulses for furthersupplying said rails with feed back energy in the form of pulses thatrecur in step with said master code off periods, a detector relay fordistinguishing between vacant and occupied conditions of said section,and means controlled by said coding device for (l) connecting saiddetector relay with said rails during each of said master code offperiods whereby under said vacant section conditions the detector relayreceives and responds to the said pulses of feed back energy which thoserails then transmit and (2) maintaining said detector relay disconnectedfrom the section rails during each of said master code on periods plusthe early portion of each following off period whereby at all times thedetector relay is prevented from receiving either the master energy ofsaid on period pulses or the master energy potential that under occupiedas well as vacant conditions of said section may be stored in said railsat the beginning of each of said off code periods.

6. In combination, a section of railway track, means including a codingdevice for supplying the rails of said section with master code energyin the form of recurring on period pulses that are separated by olfperiod intervals, means effective under vacant conditions of saidsection and governed by said on period master energy pulses for furthersupplying said rails with feed back energy in the form of pulses thatrecur in step with said master code off periods, a detector relay fordistinguishing between vacant and occupied conditions of said section, arepeater relay controlled by said coding device and occupying a rstposition during each of said master code on periods but shifting after ashort delay to a second position upon the occasion of each of saidmaster code off periods, and means including a contact of said repeaterrelay that is closed in said second position and open in said rstposition for connecting said detector relay with said rails during andonly during the concluding portion of each of said master code offperiods whereby under said vacant section conditions the detector vrelayreceives and responds to the said pulses of feed back energy which thoserails then transmit andwhereby at all times the detector relay isprevented from receiving master energy storage potential that underoccupied as well as vacant conditions of said section may be presentbetweenfsaid rails during the early portion of each of said off codeperiods.

'7. In combination, a section of railway track, a source of mastercontrol energy for said section, a detector relay for distinguishingbetween vacant and occupied conditions of said section, a coding devicehaving contacts which repeatedly shift from a front to a back and fromsaid back to said front position, a contact of said device which in agiven one of said two positions connects the section rails with saidsource and thereby causes those rails to receive an on period pulse ofmaster code energy and vwhich in the other of said positions interruptsthat connection and thereby produces a master code off period, meanseffective under vacant conditions of said section and governed by ysaidon period master energy pulses for further supplying'said rails withfeed back energy in the form of pulses that recur in step with saidmaster code off periods, a repeater relay controlled by said codingdevice and occupying a first position during each of' said master codeon periods but shifting after a short delay to a'second position uponthe occasion of each of said master code off periods, and meansincluding a contact of said repeater relay that is closed in said secondposition and open in said first position for connecting said detectorrelay with said rails during and only durthe concluding portion of eachof said master code oily periods whereby under said vacant sectionconditions the-detector relay'receives and responds to the said pulsesof-feed back energy which those rails then transmit and whereby at alltimes'the detector relay is prevented from receivin'g masterenergystorage potential that under occupied as well as vacant conditionsof said section may be present between said rails during the earlyportion of each of said off code periods.

8. In combination, a section of railway track, a

source of master control energy for said section, a detector relay fordistinguishing between vacant and occupied conditions of said section, acoding device having contacts which shift from a front to a back andfrom said back to said front position repeatedly and in synchronousrelation with respect to each other, a repeater relay energized over oneof said coding device contacts and being picked up when that contact isin its front position but releasing after a short delay upon eachtransfer of that contact to its back position, a circuit which iscompleted only when another contact of'said coding device is in itsfront position at a time when a contact of said repeater relay is pickedup and over which the rails of said section are supplied with mastercode energy that is derived from said control source and that is in theform of recurring on period pulses that are separated by off periodintervals, meanseffective under vacant conditions of said section andgoverned by said on period master energy pulses for further supplyingsaid rails with feedback energy in the form of pulses that recur in stepwith said master code off periods,

and a circuit completed only when a contact of said repeater relay isreleased for connecting said sensei detector relay with'said railsdturing each of said master code off periods but not until after theinitial portion thereof whereby under said vacant section conditions thedetector relay receives and responds to the said pulses of feed backenergy which those rails then transmit and whereby at all times thedetector. relay is prevented from receiving master energy storagepotential that under occupied as well as vacant conditions of saidsection may be present between said rails during the early portion `ofeach of .said oi code periods. f

9. In combination, a control circuit comprising a pair of conductors,means including a coding device for supplying said lconductors withmaster code energy in the form of recurring fon period pulses that areseparated by off period intervals, means governed by said on periodpulses of master energyrforfurther supplying said conductors with'feedback energy in the form of momentary pulses that recur in step with saidmaster code off periods, a repeater relay controlled by said codingdevice and occupying a rst position during each of said master codeVof-f periods but shifting to a secondV positionrupon the occasion ofeach of said masterrcode on periods, a code following detector relayprovided with a pick-up winding and with a stick circuit, meansincludingl a first contact of said repeater relay that is closed only insaid first position forV connecting said pick-up windingwithsaidconductors during each of said master codefof? periods whereby thedetector relay receives Vand is picked up by each of the said feed backenergy pulses which those lconductors transmit, means including a frontcontact of said detector relay and a second contact of said repeaterrelay that is closed only in said rst position forY completing saidstick circuit from the time of each pick-up 0f the detector relay untiltheend of the off code period within which that pick-up occurs wherebyto prolong the hold-up time of the detector relay for the full durationof each of those off code periods, and apparatuscontrolled by saiddetector relay and distinctively responsive according as that relay isoris not recurrently picking up and releasing.

10. Incombination, a section of railway track, means including a codingdevice for supplying the section rails with master code energy in theform of recurring on period pulses that are separated by off periodintervals, meansreffective under vacant conditions of said section andgoverned by said on period master energy pulses for further supplyingsaid rails with feed back energy in the form of momentary pulses thatrecur in step with said master code off periods, a repeater relaycontrolled by said coding device and occupying arrst position duringeach of said master code 01T periods but shifting to a second positionupon the occasion of eachrof said master code on periods, a codefollowing detector relay provided with a pick-up winding and with astick circuit, means including a contact of said repeater relay that isclosed only in said first position for connecting said pick-up windingwith said rails during each of said master code 01T periods whereby thedetector relay receives and is picked up by each of the said feed backenergy pulses which those rails transmit, means including a frontcontact of said detector relay and a contact of said repeater relay thatis closed only in said'iirst position for completing said stick circuitfrom the time of each pick-up of the detector relay until the end of the01T code period Within which that pick-up occurs whereby to prolong thehold-up time of the detector relay for the full duration of each ofthose off code periods, and traffic governing apparatus controlled bysaid detector relay and distinctively responsive according as that relayis or is not recurrently picking up and releasing.

ll. In combination, a section of railway track, a source of mastercontrol energy for said section, a coding device having contacts whichrepeatedly shift from a front to a back `and from said back to saidfront position, arepeater relay energized over a contact of said codingdevice and being released Whenthat contact is in its back position butpicking up after a short delay upon each transfer of that contact to itsfront position, a circuit which is completed only when a contact of saidcoding device is in its front position at a time when a contact of saidrepeater relay is picked up and over Which the i.

rails of said section are supplied with master code energy that isderived from said control source and that is in the form of recurringon" period pulses that are separated by off period intervals, meanseffective under vacant conditions of said section and governed by saidon period master energy pulses for further supplying said rails withfeed back energy in the form cf momentary pulses that recur in step withsaid master code oit periods, a code following detector relay providedwith a pick-up winding and with a stick circuit, means including a backcontact of said repeater relay for connecting said pickup Winding withsaid rails during said recurrent off code periods whereby the detectorrelay receivesl and is picked up by each of the said feed back energypulses which these rails transmit, means including a back contact ofsaid repeater relay and a front Contact of said coding device forcompleting said stick circuit from the time of each pick-up ofthe'detector relay until the end of the oif code period Within whichthat pick-up occurs whereby to prolong the hold-up time of the detectorrelay for the full duration of each of those off code periods, andapparatus controlled by said detector relay and distinctively responsiveaccording as that relay is or is not recurrently picking up andreleasing.

HERMAN G. BLOSSER.

